第一型天然氣水合物儲集層之模擬設計比對研究

• Main Authors: 吳政岳, Wu, Cheng-Yueh
• Other Authors: 資源工程學系, 謝秉志, Hsieh, Bieng-Zih
• Format: Thesis
• Language: English
• Published: 2018
• Subjects: 油相水合物; 固相水合物; 相對滲透率; 沉陷量; Oil-phase designed hydrate; Solid-phase designed hydrate; Relative permeability; Subsidence; permafrost
• Online Access: http://ir.lib.ncku.edu.tw/handle/987654321/177352; http://ir.lib.ncku.edu.tw/bitstream/987654321/177352/1/index.html

為了使台灣能達到低碳排放的目標，未來的能源政策主要仰賴潔淨能源，其中包含再生能源與低碳能源。除了發展再生能源(如太陽能、風能)之外，台灣將增加天然氣發電的使用來達到低碳排放的目標。在台灣西南海域曾發現的大量天然氣水合物資源將成為台灣能源自主的新契機。 天然氣水合物是存在於低溫高壓狀態下的固態冰晶狀能源礦物，主要存在於永凍層與海洋沉積環境中。第一型天然氣水合物儲集層為含有氣層的水合物儲集層，是目前公認最具有生產潛力的礦區種類。在水合物的生產方式中，降壓生產是迄今公認最具經濟開採水合物的方式。在此工法中，地層壓降程度是水合物分解效率的重要指標，但是當地層孔隙壓力降低使水合物分解時，也會造成地層岩石受到更多的應力並可能發生地層形變。因此，天然氣水合物在生產開發前需要審慎評估。 數值模擬法是石油工程業界常用於評估油氣資源的方式，在水合物的模擬研究中，CMG公司開發的STARS模擬器是經驗證具備模擬天然氣水合物生產開發技術的模擬軟體。但在文獻中，水合物在STARS模擬器中多假設為黏稠油的相態，以模擬水合物在地層中不會流動的現象。由於水合物在實際狀態下為固態，因此本研究的目的為比較不同相態設計的水合物在第一型天然氣水合物礦區下的生產行為，並進一步討論不同相態水合物設計對於地層變形量的影響。 本研究依照文獻設計一口垂直井，穿孔於第一型水合物的氣層高區中。藉由改變水合物的相態設計，比較並校正固相水合物於數值模擬中的正確性，之後加入岩石力學模組，以評估不同相態水合物設計對於地層沉陷量的影響。研究結果顯示，油相水合物對於流體的流動行為有較佳的描述能力，因此將水合物以固相進行模擬時，需使用油相水合物進行相對滲透率的校正。在岩石力學模擬上，本研究結果顯示，固相水合物對能充分考慮水合物的岩石力學特性。因此，若進行水合物的岩石力學模擬，則固相水合物是較佳的水合物相態設計。 The future energy policy of Taiwan is going to heavily rely on the clean energy including renewable and low-carbon energies to meet the target of mitigating CO2 emission In addition to developing the renewable energy like solar and wind resources Taiwan will increase the natural gas consumption to obtain enough electrical power with low-carbon emission The vast resources of gas hydrates recognized in southwestern offshore Taiwan makes a great opportunity for Taiwan to increase energy independence resources in the future Gas hydrates are crystalline energy resource which are formed when methane and water mixtures are subjected to high pressure and low temperature conditions Gas hydrates can be found in subsurface geological environments of deep-sea sediments and permafrost regions where the presence of in-situ hydrates had been confirmed by many exploration activities around the world Class-1 hydrate deposit is recognized as the largest potential to be developed in the future because there is a free gas zone under the hydrate storage area Of all the production methods in gas hydrate production depressurization is the most promising method to economically produce gas from hydrate deposits In depressurization the dissociation efficiency will be affected by the pressure drawdown disturbance However when the pore pressure of hydrate deposits is depressurized for gas production the rock matrix will surfer more stresses and the formation deformation might be occurred Numerical simulation is a common method used in the petroleum industry to evaluate the petroleum resource before development In gas hydrate numerical simulation STARS simulator which was developed by CMG Ltd had been proven to be capable to simulate the hydrate dissociation behavior and gas production from hydrate In the literature studies hydrate was set as a heavily viscos oil-phase to simulate its immobility in STARS However gas hydrate is solid-phase in practice The purpose of this study was to analyze the difference between oil-phase and solid-phase designed hydrate models in Class-1 hydrate deposit The geomechanical effects on both models were also well discussed in this study A vertical well perforated at the top of the gas zone in a Class-1 hydrate deposit was designed based on the literature study The production behavior of oil-phase and solid-phase designed hydrate were well discussed and the solid-phase designed hydrate was calibrated to obtain an accurate result After that the geomechanical module was introduced and the calculated subsidence between different phase design in gas hydrate were compared The results show that the oil-phase designed hydrate model has a better description on fluid flow behavior than the solid-phase designed hydrate model As the solid-phase designed hydrate was applied in the simulation the relative permeability should be calibrated In geomechanical effects the solid-phase design prefers for considering the geomechanical characteristics of gas hydrate If the geomechanical mechanism is considered in the simulation model solid-phase designed hydrate is suggested